In the polyisoprenoid biosynthesis pathway, 3-hydroxy-3-methylglutaryl CoA reductase (hereunder also referred to as HMGR or HMG-CoA reductase) is a rate-limiting enzyme in isoprene monomer (isopentenyl diphosphate) biosynthesis. It is known that the enzyme activity of HMGR is controlled by reversible post-translational phosphorylation, and specifically, inactivation of enzyme activity by C-terminal serine phosphorylation is well known as a post-translational regulatory mechanism of HMGR in animals. This has also been confirmed in plants, and in Non Patent Literature 1 in particular, reduced enzyme activity due to phosphorylation of the residue serine 577 corresponding to the C-terminal serine is confirmed in Arabidopsis thaliana. 
Methods also exist for increasing polyisoprenoid yield without genetic recombination, such as methods of increasing polyisoprenoid yield using cholesterol biosynthesis inhibitors, but there is still room for improvement in methods for increasing polyisoprenoid yield and the like and there is a need for the development of further technologies.